The present invention relates to a circuit breaker used for a circuit breaker of a low-voltage circuit, a ground leakage interrupter, and the like. More specifically, the present invention relates to a switching device provided in a circuit breaker and having an isolation function for preventing an operation handle from moving to an off position when main-circuit contact points are stuck together due to an abnormal current.
A basic configuration of a circuit breaker to which the present invention is applied is shown in FIG. 6. In FIG. 6, reference numeral 1 denotes a case (resin case) of a circuit breaker; reference numeral 2 denotes a main-circuit terminal on a power-source side; reference numeral 3 denotes a main-circuit terminal on a load side; reference numeral 4 denotes a fixed contact; reference numeral 5 denotes a movable contact; reference numeral 6 denotes a circuit interrupter; reference numeral 7 denotes a contact holder of the movable contact 5; reference numeral 8 denotes a switching device; reference numeral 9 denotes an operation handle; and reference numeral 10 denotes a bimetal-type over-current tripping device.
The switching device 8 has a side plate (assembly frame of the switching device) 17. The side plate 17 supports a swing-type handle lever 11 connected to the operation handle 9; a toggle linkage 12 having an upper toggle link 12a and a lower toggle link 12b connected with a connecting pin 12c and bridging the contact holder 7 of the movable contact 5 and a latch (trip lever) 13 through pin connection; a latch receipt 15 combined with a trip cross bar 14 for locking the latch 13 in a normal state and for releasing the latch 13 in response to a movement of the over-current tripping device 10; and a switching spring (tension coil spring) 16 placed between a base (upper side) of the handle lever 11 and the connecting pin 12c of the toggle linkage 12.
An operation of switching the circuit breaker is commonly known. When the handle 9 is moved from an “on” position to an “off” position, the switching spring 16 passes over a dead point and is reversed. Accordingly, the upper toggle link 12a and the lower toggle link 12b of the toggle linkage 12 are folded into a shape of the symbol “<” with a spring force of the switching spring 16 to open the movable contact 5.
When an over-current flows during electrification and the over-current tripping device 10 is activated, the latch 13 is released via the trip cross bar 14 from a state that the latch 13 engages the latch receipt 15. As a result, the movable contact 5 is opened by the spring force of the switching spring 16 to shut down the current (tripping). When the tripping occurs, the operation handle 9 moves to an intermediate position between the “on” position and the “off” position together with the handle lever 11 to indicate the tripping. When the circuit breaker is turned on again after the tripping, the handle 9 is moved to the “off” position, i.e. a reset position, to engage the latch 13 with the latch receipt 15. Then, the handle 9 is moved back to the “on” position to close the movable contact 5.
In the circuit breaker described above, the fixed contact and the movable contact may be stuck together when an abnormal current flows through the main circuit in an electrification state in which the main-circuit contact points are closed. In this case, even through the over-current tripping device 10 is operated normally, the movable contact 5 is not opened, and the operation handle 9 remains at the “on” position.
In the switching device described above, it is possible to move the handle 9 from the “on” position to the “off” position by applying a large force thereto, even when the main-circuit contact points are stuck together. Therefore, when the contact points are stuck together, an operator can move the handle to the “off” position and lock the handle with a padlock or the like without knowing the occurrence of the abnormal event. In this case, the operator may touch a hot line and suffer an electric shock, if the operator mistakenly confirms that the breaker is turned off and performs a check and maintenance of the circuit on the load side.
Moreover, the operation handle 9 of the circuit breaker may be provided with an external operation handle device driven by a motor, so that the operation handle 9 can be switched through remote control. In this case, when the operation handle 9 is moved to the “off” position, the external operation handle device sends a breaker-off signal and locks the operation handle 9 in the “off” position. For this reason, if an abnormal current flows and the contact points are stuck, the operator mistakenly confirms that the breaker is turned off, thereby causing a safety issue.
As a countermeasure against such a problem, a configuration is known in which the circuit breaker is provided with an isolation function for preventing the handle from moving to the “off” position when the contact points are stuck together during the electrification. In a specific configuration, the contact holder 7 of the movable contact 5 and the handle lever 11 are provided with abutting stoppers having protrusion shapes, respectively. With this configuration, when the operator intends to move the operation handle 9 to the “off” position in a state that the contact points are stuck together, the abutting stoppers abut against each other to prevent the handle from moving to the “off” position (refer to Japanese Patent Publication (Kokai) No. 05-182577).
A conventional switching device having such a mechanism is shown in FIG. 7. In FIG. 7, the operation handle 9 is moved to a dead-point position (described later) from the “on” position, in a state that a contact point 4a of the fixed contact 4 and a contact point 5a of the movable contact 5 are stuck together. In the switching device shown in FIG. 7, an abutting stopper 11a protruding toward the contact holder 7 is formed at an end of the handle lever 11, i.e. a position shifted to the right side from a rotational center 0 (on the “off” position side of the operation handle 9). An abutting stopper 7b facing the abutting stopper 11a is formed on a peripheral surface of the cross bar 7a of the contact holder 7 (a rotary shaft of the holder).
The handle lever 11 is formed in a branched shape having an upper base connected to the operation handle 9. A concave groove is formed at an end of the handle lever for receiving a bearing part 17a having an L-shape protrusion and formed in an outer surface of the side plate 17, so that the handle lever 11 is rotatably supported. The switching spring (tension spring) 16 holds the handle lever 11 at an assembled position. In general, the handle lever 11 adopts such a support structure in consideration of ease of assembly of the switching device.
“ON” and “OFF” shown in FIG. 7 denote an “on” position and “off” position of the operation handle 9 relative to a reference line (an projected line on the swing fulcrum of the handle lever 11), respectively. Further, “DP” denotes a dead point at which the operation handle 9 transits from the “on” position to the “off” position (a state in which the switching spring 16 is in a neutral position relative to the toggle linkage 12). Furthermore, “SL” denotes an action line of the spring 16 placed between the connecting pin 12c of the toggle linkage 12 and an upper side of the handle lever 11. As shown in FIG. 7, the action line “SL” is on the dead point of the toggle linkage 12 (on a line between the connecting pin 12c of the toggle linkage 12 and a connecting pin 12d of the latch 13 of the upper toggle link 12a).
In the structure described above, in the state that the contact points are stuck, when the operator attempts to move the operation handle 9 from the “on” position to the “off” position, the abutting stopper 11a of the handle lever 11 abuts against the abutting stopper 7b of the contact holder 7 situated at the closed position of the contacts at a point that the operation handle 9 is slightly beyond the dead point DP of the handle, so that the operation handle 9 is prevented from moving to the “off” position.
In the conventional structure shown in FIG. 7, there are the following problems concerning an operation of the isolation function.
As shown in FIG. 7, the concave groove formed at the end of the handle lever 11 receives the bearing part 17a formed on the outer surface of the side plate 17 to rotatably support the handle lever 11. In this structure, the abutting stopper 11a of the handle lever 11 abuts against the abutting stopper 7b of the contact holder 7, thereby preventing the operation handle 9 from moving to the “off” position. In this state, when the operator intends to further move the operation handle 9 by applying a large force thereon, the concave groove at the end of the handle lever 11 moves upwardly out of the bearing part 17a. Accordingly, the operation handle 9 moves to the “off” position around the abutting point of the abutting stoppers 11a and 7b. 
In the configuration described above, when the operation handle 9 moves to the “off” position, the abutting stoppers 7b, 11a abut against each other after the action line of the switching spring 16 passes the dead point DP shown in FIG. 7, so that the abutting stoppers 7b, 11a do not interfere with each other in the normal “on” and “off” operations. Further, in the state that the contact points are stuck, when the operator releases the operation handle 9 at a position in which the abutting stoppers 7b, 11a abut against each other to prevent the operation handle 9 from moving, the operation handle 9 returns to the “on” position.
There may be a case that the “off” position of the operation handle 9 is situated close to the DP position depending on an assembly structure of the switching device or due to a play between components. In such a case, when the operation handle 9 is moved toward the “off” position in the state that the contact points are stuck, the handle 9 may easily return to the “off” position from the DP position before the handle 9 is securely prevented from moving.
The operation handle 9 may be locked at the “off” position with a padlock, or the operation handle 9 may be provided with an external operation handle device. In such a case, when the operation handle 9 is moved toward the “off” position in the state that the contact points are stuck, the handle 9 is locked at the “off” position even though the main circuit points are closed, so that the operator mistakenly confirms that the contact points are opened.
In view of the problems described above, the present invention has been made, and an object of the invention is to provide a circuit breaker having an improved configuration relative to the conventional device. In the circuit breaker of the invention, it is possible to securely prevent the operation handle from moving to the “off” position even though the contact points are stuck. Also, it is possible to stabilize the isolation function of the circuit breaker.
Further objects and advantages of the invention will be apparent from the following description of the invention.